Radio-frequency network



NW 30, 1948. R N 2,454,907

RADIO FREQUENCY NETWORK Filed Nov. 21, 1945 ull-1 v -INVENTOR. @3531 fimgefi. Brown ATTORZVEZ Patented Nov. 30, 1948 RADIO-FREQUENCY NETWORK George H. Brown, Princeton, N. J., assignor to Radio Corporation of of Delaware America, a corporation Application November 21, 1945, Serial No. 630,073

This invention relates to radio frequency'power networks wherein two independent sources, which must be electrically isolated from one ariother, are required to supply energy simultaneously to a common load device. Networks of the described type find application, for example, in television broadcast systems, wherein it is desired to transmit a picture" signal and an accompanying sound signal from a single antenna. In order to prevent interchange of power between the sound and picture transmitters, it has been the practice to employ filters. Such filters require careful design, will operate only with sound and picture carrier frequencies for which they are designed, cause a certain amount of loss, and introduce reactances in'the system which make it difiicult to design the overall system for efiicient broad band operation which is necessary for high definition television. 7

It is the principal object of the present invention to provide a radio frequency network which will substantially isolatetwo sources from each other, while enabling them to supply common loads simultaneously.

Another object is to provide a system of the described type which does not. rely upon'filters or equivalent means for the function of isolation, and thus introduces a minimum of undesirable reactance in the system.

Another object is to provide an isolation network coupling a single antenna system to a transmitter and another transmitter or a receiver for operation independently of one another. y 1

A further object of this invention is to provide an isolation network which is readily adaptable to the requirements of combined sound and television broadcasting.

Still another object is to provide a network of the described type which is conveniently applicable to antennas of the type including two separately excited groups of radiators, such as the turnstile. J a

The invention will be described with reference to the accompanying drawings, of which Figure 1 is a schematic diagram of an isolation network according to the invention,

Figure 2 is a schematic diagram of a sound and television broadcast antenna system embodying an isolation network in accordance with the invention."

Refer to Figure 1; jA'pair of identical loads, represented by equal resistors] and 3, are to be energized simultaneously and independently from sources 5 and 1. The lower end of each 3 Claims. (Cl. 250-33) of the resistors is grounded; i. e. they are unsymmetrical or unbalanced to ground. The generators 5 and l are similarly unbalanced to ground. From a practical standpoint, this means that coaxial transmission lines may be used for the connections to the elements l, 3, 5 and l.

A coaxial line 9 is connected to the generator 5. A portion ID at the end of the line 9 remote from the generator 5 is surrounded by a coaxial sleeve ll of conductive material. The lower end of the sleeve H is connected to the outer conductor of the line 9 at their junction l3. The upper end portion of the outer conductor of the line section It is provided with a slot 15 extending diametrically across the line and longitudinally down to the point H. The upper end of the inner conductor is connected to that of the outer conductor at one side of the slot 15.

The loads l and 3 are'connected to the end of the outer conductor of the line section ill, on opposite sides of the slot Hi. The generator 1 is connected to the outer conductor of the line section H3 at'a point l-9 below the bottom I! of the slot l5.

'The operation ofpthe system of Figure 1 is as follows:

The slot l5 extends longitudinally down the line section. l0 one-quarter wavelength at the mean frequency of operation of the system. When current at said frequency is supplied to the line 9 by the generator 5, the instantaneous current flow is up' the inner conductor of the line 9 to the upper end of the outer conductor, at the right hand side of the slot It.

The two parts of the outer conductor separated by the slot I5 cooperate to act as a quarter Wavelength open wire line, short-circuited at the point N. This presents a substantially infinite impedance between the upper ends of the two portions of outer conductor and effectively prevents any of the current from the inner conductor from flowing down the outer conductor. Thus if a current I is flowing up the line 9 from the generator 5, the same current I flows into the, load 3. l h

The current I flowing up the inner conductor ofthe line 9 is balanced by an equal current returning down the inside of the outer conductor of the line 9. This current flows up through the load I to the upper end of the outer conductor of the line section H1, at the left hand side of theslot l5. Owing to the high impedance across the upper end of the slot, all of this current flows down inside the left hand portion of the outer conductor, spreading over the interior reducing the total current which flows from the v load i to its point of connection. Thus the cur- H rents to the two loads remain equal to each other, but they are no longer the same as-that flowing up the line 9. The =-net "eiftect is somewhat similar to that of shunting the generator by the reactance of the parallel wire line section formed by the two end portionsof the-ceremonductor of the section l0.

The outer conductor of the line section if! cooperates with the sleeve H to function as a co axialline section short-circuited at its lowergend l3. Current from the generator I is applied to this'line section atthe pointIS. This currentinduces a voltage along the outside of the outer conductor of the section Ill by autotransformer action. The voltage to ground fromboth arms of the outer conductor'is the same. Thus the voltage betweenthe ends of the outer conductor is zero, and-no current is induced in'the line 9 'byith'e generator A *Since the two'ends of the outer conductor are at'the same voltage with respect toground, equal currents iio'w from them through the -load resistorsl andt. These-currents are in p h'ase with each other, as indicated -'by the dash arrows. None "of the'current fromthe generator :5 flows on' the outside of the outer conductor of the line section iih'sono current is-induced inthegenerator '1 by the generator'i Thus bothloadsare energized by each generator wit'hout interaction.

"-The above described system maybe applied to advantage in a combined "television and sound transmission system wherein a single antenna system is used. Referring to :Figure' Z, an antenna of the'turnstile'typ'e, o'oinprising four orthogonally disposed radiator arms N, S, E-and -W, is;to be energized simultaneously by'a sound transmitter 2| and a picture transmittenfi. The radiator pair N-S is to be excited :as a'dipole, and the otherpair E W as;another dipole in quadrature phase with respect to the first. 'In Figure 2 all coaxial lines are represented as-single lines; whose connections correspond to those oftheinnerconductors of the actual coaxial lines. All of the outer conductors are connected together and grounded.

The radiators N- and S areconnected together by'a line 25. A feed line 21 is connected to the line 25 at a point 29 one-quarterwavelengthirom the midpoint of the line-25,--so thatthe distance from the point 29 to theradiator'N isone-half wavelength diiierent from the distance between the=point29 and the radiator' s; The radiators E and W are similarly connected together bya li-ne 3|, tapped one quarter wave on center at the point 33, where '=a second "feed line =35-is c'onnected.

The line "21 none-quarter wavelength longer than the'line 35. The lines 21- and35 areconnected like the loads *1 and-3 in the systr'hdf Figure 1 to a network 31, identical Withthestructure shown in Figu're I. The pictuie traiismitter 23 is connectedtothe network t'llikethe genera 4 tor 5 of Figure 1, and the sound transmitter 2! is connected like the generator I of Figure 1.

In the operation of the system of Figure 2, the feed lines 21 and 35 are supplied like the loads l and 3 in Figure 1, out of phase by the transmitter 23 and in phase by the transmitter 2!. Energy travels up the line 21 to the point 29. From =this -point,ait'--reaches the radiator S over a path 'o'ne hailf Wavelength longer -thanlthepath to the radiator N. Thus current flows in on the radiator S while current is flowing out on the radiator N, and vice versa, exciting the radiators N and S as elements "of a dipole.

The radiator elements E and W are excited similarlygby energy flowing up the line 35. Since the linert'lisene quarter wavelength longer than the line35, the currents in the dipole N-S are induadratiifephasewith the corresponding currentsin the dipole EW.

The efiect of feeding the lines 21 and 35 in push-pull frqm-thetransmitter -23-and in the same phase from the transmitter 2| is' merely to cause the phase rotatidnpi the'turnstileto be-in one direction (e.-g.clockwise) for theoutput of the soundtr-anshiitter and-in the opposite direction for the; picturesignal.

Although a relatively "simple antenna system liaslieen illustrated to show a typical application ofth'e present invention, it will be understood by those skilledi-n the art that it is not'restricted thereto, but maybe" applied equally well-to any systemwherem separate load elements are to be excited simul'taneous'ly "by two sources without interaction.

I'claiin as my invention:

antenna system including an isolation networ "com rising affirst coaxial input line, a conductive sleeve surrounding one end of said nneendtonncteu' toitljie outer conductorof said line at a point near'said en'd, theend portionof the cuterccnductcr (if said line including alongituiiihalslotfthe end (if the inner conductor of said linebeix 'gcoi'ii fe'ctedto' tli'ele'nd of the outer conductorc'i'f said'lineat'hne side only of said slot, a second coaxial input line with its outer conductor connected to said sieev and its inner conductor coupledt the uter'cdnductor'of said'firstiinput linewitliifis'ai s are, and a pair of coaxial output'lineswiththeir'outer conductors connected'to said sleeve and their-inner conductors connected to the "'ifd of the outer conductor of said -first input line io'n; opposite sides respectively of said slet, dipole radiator means-coupledto one of said outputdine's, 'andiiifther dipole radiator means at right angles to said first-radiator means and ceupledto the "other df-seiidoutput lines, one of said 7 output lines being one-quarter wavelength longer'than'the'other.

-2. An'iso1ation networl z for radio frequency power systems including a=first coaxial input line, a conductive sleeve surrounding one end i ofsaid line andconneoted to -the outerconducton of said line at a point near said end, the end portion of the outernoonductor pf said line including a longitudinal slot; the en'd' of th'eiiniiefc'ofiduetor ofsaid line being 'connected to the ndof the outer conductor of said line at e'ne si'de-only of s'a'id slot, a seccr-ia ecaxiarrnput line with its-outeri'conreconnected V aidfsleeveanditsinnerconduetor coupled totheouter conductor of said' first input line Withinsaid sleeve, and a pair oif'ccaxial output lineswith their outer conductorscofinected to said sleeve a'rfd f their innerc nductors connectifto fthe'iendof theouter'fcdfiductor cfisai'd 5 first input line on opposite sides respectively of said slot.

3. An isolation network for radio frequency power systems including a first coaxial input line,

a conductive sleeve surrounding one end of said 5 said sleeve, and a pair of loads, each connected between said sleeve and the end of the outer conductor of said first input line, on opposite sides respectively of said slot.

GEORGE H. BROWN. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,286,179 Lindenblad June 9, 1942 2,318,237 Lin-denblad May 4, 1943 

